1. Field of the Invention
The present invention relates to a selectively, partially hydrogenated polymer, and to a rubber composition and an impact resistant styrenic resin containing the same. More specifically, it relates to a selectively, partially hydrogenated butadiene polymer having a specific structure and a composition thereof comprising a butadiene polymer, e.g., a butadiene homopolymer or a styrene-butadiene copolymer having a specific structure which is partially and selectively hydrogenated, and to a rubber composition and an impact resistant styrenic resin containing the same.
2. Description of the Related Art
Polymers obtained by partial hydrogenation of styrene-butadiene copolymer have long been known, and it has been proposed to obtain a composition having an improved green strength by blending this polymer with other diene type elastomers or ethylene-propylene copolymer rubbers (JP-B-46-35497). Proposals have been also made for a composition having an excellent strength at break, and a rubbery elasticity, comprising this polymer and a specific inorganic filler (JP-B-47-8928), and for a method for producing an oil-extended rubber having an excellent heat-resistant aging characteristic and resilience (JP-B-46-29020) and the like.
Nevertheless, when the catalyst composed mainly of organic compounds of iron, nickel, cobalt of the prior art is used, it is difficult to partially hydrogenate the vinyl linkage by preferential selection, and to hydrogenate the vinyl linkage to a high extent, the 1,4-linkages including the cis-linkage and translinkage also must be hydrogenated to a high degree. This method also generated crystalline copolymers, and the intended improvement of resilience and heat-resistant aging characteristic resulted only in an undesirable marked increase in the hardness or a lowering of the exothermic property.
A method has been also proposed in which only the side chain portion of a diene polymer (i.e., vinyl linkage portion in butadiene polymer) is selectively hydrogenated, and a method is also known of obtaining a selectively hydrogenated diene polymer having an ozone resistance and an oxidation stability (JP-A-52-41690). But the polymer obtained according to this method, although showing a slightly improved heat-resistant aging characteristic or resilience, does not have a sufficient improvement of such characteristics, and no improvement at all of the hardness and elasticity modulus was observed.
As one of the many utilizations of unvulcanized rubber, the unvulcanized rubber is employed as a toughening agent for alleviating the brittleness of styrenic polymers such as polystyrene.
As the unvulcanized rubber used thereby, polybutadiene rubber and styrene-butadiene copolymer rubber are generally employed, and in particular, a low-cis polybutadiene rubber polymerized by using an organic lithium compound is used. Also, in some cases, a high-cis polybutadiene rubber polymerized by using a transition metal compound of, for example, cobalt, as the main component may be used. Nevertheless, the conventional impact resistant styrenic resins do not have a sufficient impact strength, and the development of resins having a greater impact resistance, and toughening agents therefore, are sought.